Imagine digital radio transmissions on the AM band not just at the 50 KW level we�re familiar with in the U.S. � but at the 100, 200, 300 KW level and higher.� That�s what�s going on in India now, as the Public Broadcaster All India Radio upgrades their terrestrial transmission systems across the country.�Digital Radio Mondialetechnology is used for the digital modulation.�
We�ve previously reported on the deployment of Nautel transmitters in India (hereandhere) and knowing the readers of DRU will be interested in high-power applications, we sought out the project manager for Nautel�s All India Radio project, Stephen Farley, who was kind enough to take time out of his schedule to answer.
Doug Irwin: This is a very high power application, so I�d be curious to know about the transmitter types.� Are you using something like 100 KW versions, and then big combiners?
Stephen Farley: The transmitter systems used for the All India Radio contract are all based on Nautel�s proven NX series of transmitters. The NX Series are all discrete transmitter designs for 100, 200, 300 and 400 kW. Using these transmitter building blocks Nautel can achieve even higher power levels up to 2 Megawatts using combining technologies. So to be clear the 11 100kW, 10 200kW and 6 300kW NX transmitters delivered to AIR are all �discrete� transmitters in themselves, with one combiner and output filter. Only above 400kW do we start to need separate combiners.
DI: Does AIR simply use non-directional antennas?� Are there any issues with antenna bandwidth related to DRM-type modulation?
SF: Many antennas are Omni directional with close to Ideal tower heights and are mostly suitable for the DRM performance. That said this has been one the most challenging parts of the project and Kintronics Labs were commissioned to produce ATU�s to give us the maximum performance possible. There are variants with driven directional and parasitic directional. AIR is using 20 KHz active bandwidth during the transition phase. The station frequency for analog and its bandwidth has been retained. The DRM signal is positioned on the upper side of the bandwidth. �There are total of 3 driven directional sites and 5 parasitic directional sites.
DI: How does AIR distribute their network programming?
SF: I�ve learned from our Indian representative that there are a few methods used by AIR. For example they have dedicated satellite links available for their use. The use microwave STL for the main. They do use fiber links and some IP based links. They create the linking in real time and do not follow store and transmit mode. Some stations are networked and Main news is always networked from New Delhi.
DI: Every project comes with good stories.� Any you care to tell us?
SF: As part of the project Nautel has partnered extensively with Comcon Industries, of New Delhi, headed by Rakesh Aggarwal. We trained personnel from Comcon on the systems and they have become our �front line� team during the installation and commissioning process. This �in-country� team have proved invaluable in keeping up the momentum of the commissioning process; being on hand, in the same time zone, to answer questions from the AIR installation teams, move quickly to the different sites, as needed, for commissioning or training. We now have about 23 of the 27 sites on air, which is some sort record for AIR, with such a large project. This success has transferred into our opening of a dedicated Nautel Service Centre India, with dedicated in-country email and phone support from the India team, headed by Trinayan Goswami of Comcon.